The usual mode of procedure in a spinning mill is that the fibrous material mixed with impurities is subjected to repeated cleaning in the cleaning room and the carding department before it reaches the further processing machines. The cleaning of the fibrous material in the usual opening and cleaning machines is incomplete, however. Even after passing through the carding machines, particles of dirt and, in particular, fine and very fine dust remain in the fibrous material. Satisfactory cleaning is important, however, for the following processing, particularly when using rotor spinning machines which do not include any possibility for the removal of dirt.
Proposals for an improved opening and cleaning of the fibrous material have already been made. Thus, a saw-tooth opener is known for the opening of fibrous material, particularly cotton, wherein a beater roller which is provided with pins or teeth and rotates rapidly counter to the direction of rotation of the opening roller, and a grating associated with this are disposed between the usual opening rollers and doffing rollers to remove impurities.
The fibrous material thus treated is drawn off the doffing roller by means of a stream of air and conveyed in a collecting pipe to a cage-type air separator. It is true that such a saw-tooth opener, which is disclosed in the DT-PS 1.114.127 renders possible a separation of the fibrous material into the finest fiber flocks and individual fibers. The object aimed at, however, of removing the impurities set free, is essentially only achieved with regard to the relatively coarse impurities which rub off on the edges of the grating bars. Fine and very fine impurities, on the other hand, remain in the fibrous material so that the cleaning action of this known apparatus is inadequate.
A so-called cascade cleaner has been developed for the removal of impurities including dust (U.S. Pat. No. 3,006,034). In this case, the fibrous material is compressed at the inlet side of the machine on a cylindrical cage serving as a feed device, with an associated compression roller, and is then stripped off the cage by a stripper roller which has the same direction of rotation as the cage. The impact points of the cascade cleaner are indirectly connected to the cage through conduits in order to draw off dust from the impact points through the cage. Only a weak stream of intake air can be used for this, however, because otherwise large amounts of fibrous material would be returned from the impact points to the cage with the dust. Thus, the removal of dust is unsatisfactory.
Furthermore, an apparatus for cleaning flocks of natural fiber, such as cotton flocks, of particles of dirt is known which comprises a plurality of cylindrical cages disposed in series (DT-OS 2.431.018). It is true that the removal of dust from the fibrous material for which this apparatus is intended, is improved, but the constructional expense and the necessary suction power are disproportionately high. Since the fibrous material is exposed to the streams of intake air in the individual cages in the form of more or less fine flocks, there is no assurance that dust, particularly that present in the interior of the flocks, will be completely removed, even with a high suction power.
Finally, it is also known already to provide two lickers-in with one or more compression rollers disposed in between and possibly also squeezing rollers as a feed device for a carding machine in order to improve the opening and cleaning of the fibrous material (GB-PS 1.230.331). The increased removal of dirt possible as a result mainly extends, however, to impurities of a coarser kind while fine and very fine dust in particular, and also smaller particles of dirt and fiber fragments, remain in the fibrous material.